Electric arc welder

ABSTRACT

An electric arc welder for depositing weld metal along a groove between two edges of a metal workpiece where the welder comprises a first electrode driven by a first wire feeder toward a point in said groove, a second electrode driven by a second wire feeder toward the point and a main power source with a first output terminal connected to the first electrode and a second output terminal connected both to the second electrode and directly or indirectly to the metal workpiece to create a second electrode path and a workpiece path. The power source includes a high speed switching output stage for creating current with a selected AC waveform between the first and second output terminals where the waveform of the main power source is generated by a waveform generator controlling a pulse width modulator circuit to determine the current operation of the output stage.

The present invention relates to the art of electric arc welding andmore particularly to an electric arc welder system to operate tandemelectrodes.

INCORPORATION BY REFERENCE

The present invention is directed to an electric arc welding systemutilizing high capacity alternating circuit power sources for drivingtwo or more tandem electrodes of the type used in seam welding of largemetal blanks. Although the invention can be used with any standard ACpower supply with switches for changing the output polarity, it ispreferred that the power supplies use the switching concept disclosed inStava U.S. Pat. No. 6,111,216 wherein the power supply is an inverterhaving two large output polarity switches with the arc current beingreduced before the switches reverse the polarity. The power source canbe a chopper operated at high switching speeds. Consequently, the term“switching point” is a complex procedure whereby the power supply isfirst turned off awaiting a current less than a preselected value, suchas 100 amperes. Upon reaching the 100 ampere threshold, the outputswitches of the power supply are reversed to reverse the polarity fromthe D.C. output link of the inverter. Thus, the “switching point” is anoff output command, known as a “kill” command, to the power supplyinverter followed by a switching command to reverse the output polarity.The kill output can be a drop to a decreased current level. Thisprocedure is duplicated at each successive polarity reversal so the ACpower supply reverses polarity only at a low current. In this manner,snubbing circuits for the output polarity controlling switches arereduced in size or eliminated. Since this switching concept is preferredto define the switching points as used in the present invention, StavaU.S. Pat. No. 6,111,216 is incorporated by reference. The concept of anAC current for tandem electrodes is well known in the art. U.S. Pat. No.6,207,929 discloses a system whereby tandem electrodes are each poweredby a separate inverter type power supply. The frequency is varied toreduce the interference between alternating current in the adjacenttandem electrodes. Indeed, this prior patent of assignee relates tosingle power sources for driving either a DC powered electrode followedby an AC electrode or two or more AC driven electrodes. In eachinstance, a separate inverter type power supply is used for eachelectrode and, in the alternating current high capacity power supplies,the switching point concept of Stava U.S. Pat. No. 6,111,216 isemployed. This system for separately driving each of the tandemelectrodes by a separate high capacity power supply is backgroundinformation to the present invention and is incorporated herein as suchbackground. In a like manner, U.S. Pat. No. 6,291,798 discloses afurther arc welding system wherein each electrode in a tandem weldingoperation is driven by two or more independent power supplies connectedin parallel with a single electrode arc. The system involves a singleset of switches having two or more accurately balanced power suppliesforming the input to the polarity reversing switch network operated inaccordance with Stava U.S. Pat. No. 6,111,216. Each of the powersupplies is driven by a single command signal and, therefore, shares theidentical current value combined and directed through the polarityreversing switches. This type system requires large polarity reversingswitches since all of the current to the electrode is passed through asingle set of switches. U.S. Pat. No. 6,291,798 does show a master andslave combination of power supplies for a single electrode and disclosesgeneral background information to which the invention is directed. Forthat reason, this patent is also incorporated by reference. Animprovement for operating tandem electrodes with controlled switchingpoints is disclosed in Houston U.S. Pat. No. 6,472,634. This patent isincorporated by reference.

The tandem electrodes of the present invention have two leadingelectrodes as disclosed in Shutt U.S. Pat. No. 4,246,463 and in apublication by The Lincoln Electric Company of Cleveland, Ohio entitled“Another Arc Welding Development.” These items showing a modified serieslead electrode revision of a tandem arc welder, i.e. welder system, areincorporated by reference herein as background technology which need notbe revisited.

BACKGROUND OF INVENTION

Welding applications, such as pipe welding, often require high currentsand use several arcs created by tandem electrodes. Such welding systemsare quite prone to certain inconsistencies caused by arc disturbancesdue to magnetic interaction between two adjacent tandem electrodes. Asystem for correcting the disadvantages caused by adjacent AC driventandem electrodes is disclosed in Stava U.S. Pat. No. 6,207,929. In thatprior patent, each of the AC driven electrodes has its own inverterbased power supply. The output frequency of each power supply is variedso as to prevent interference between adjacent electrodes. This systemrequires a separate power supply for each electrode. As the currentdemand for a given electrode exceeds the current rating of the inverterbased power supply, a new power supply must be designed, engineered andmanufactured. Thus, such system for operating tandem welding electrodesrequire high capacity or high rated power supplies to obtain highcurrent as required for pipe welding. To decrease the need for specialhigh current rated power supplies for tandem operated electrodes,assignee developed the system disclosed in Stava U.S. Pat. No. 6,291,798wherein each AC electrode is driven by two or more inverter powersupplies connected in parallel. These parallel power supplies have theiroutput current combined at the input side of a polarity switchingnetwork. Thus, as higher currents are required for a given electrode,two or more parallel power supplies are used. In this system, each ofthe power supplies are operated in unison and share equally the outputcurrent. Thus, the current required by changes in the welding conditionscan be provided only by the over current rating of a single unit. Acurrent balanced system did allow for the combination of several smallerpower supplies; however, the power supplies had to be connected inparallel on the input side of the polarity reversing switching network.As such, large switches were required for each electrode. Consequently,such system overcame the disadvantage of requiring special powersupplies for each electrode in a tandem welding operation of the typeused in pipe welding; but, there is still the disadvantage that theswitches must be quite large and the input, paralleled power suppliesmust be accurately matched by being driven from a single current commandsignal. Stava U.S. Pat. No. 6,291,798 does utilize the concept of asynchronizing signal for each welding cell directing current to eachtandem electrode. However, the system still required large switches.This type of system was available for operation in an ethernet networkinterconnecting the welding cells. In ethernet interconnections, thetiming cannot be accurately controlled. In the system described, theswitch timing for a given electrode need only be shifted on a timebasis, but need not be accurately identified for a specific time. Thus,the described system requiring balancing the current and a single switchnetwork has been the manner of obtaining high capacity current for usein tandem arc welding operations when using an ethernet network or aninternet and ethernet control system. There is a desire to controlwelders by an ethernet network, with or without an internet link. Due totiming limitation, these networks dictated use of tandem electrodesystems of the type using only general synchronizing techniques.

Such systems could be controlled by a network; however, the parameter toeach paralleled power supply could not be varied. Each of the cellscould only be offset from each other by a synchronizing signal. Suchsystems were not suitable for central control by the internet and/orlocal area network control because an elaborate network to merelyprovide offset between cells was not advantageous. Houston U.S. Pat. No.6,472,634 discloses the concept of a single AC arc welding cell for eachelectrode wherein the cell itself includes one or more paralleled powersupplies each of which has its own switching network. The output of theswitching network is then combined to drive the electrode. This allowsthe use of relatively small switches for polarity reversing of theindividual power supplies paralleled in the system. In addition,relatively small power supplies can be paralleled to build a highcurrent input to each of several electrodes used in a tandem weldingoperation. The use of several independently controlled power suppliesparalleled after the polarity switch network for driving a singleelectrode allows advantageous use of a network, such as the internet orethernet.

In Houston U.S. Pat. No. 6,472,634, smaller power supplies in eachsystem are connected in parallel to power a single electrode. Bycoordinating switching points of each paralleled power supply with ahigh accuracy interface, the AC output current is the sum of currentsfrom the paralleled power supplies without combination before thepolarity switches. By using this concept, the ethernet network, with orwithout an internet link, can control the weld parameters of eachparalleled power supply of the welding system. The timing of the switchpoints is accurately controlled by the novel interface, whereas the weldparameters directed to the controller for each power supply can beprovided by an ethernet network which has no accurate time basis. Thus,an internet link can be used to direct parameters to the individualpower supply controllers of the welding system for driving a singleelectrode. There is no need for a time based accuracy of these weldparameters coded for each power supply. In the preferred implementation,the switch point is a “kill” command awaiting detection of a currentdrop below a minimum threshold, such as 100 amperes. When each powersupply has a switch command, then they switch. The switch points betweenparallel power supplies, whether instantaneous or a sequence involving a“kill” command with a wait delay, are coordinated accurately by aninterface card having an accuracy of less than 10 μs and preferably inthe range of 1–5 μs. This timing accuracy coordinates and matches theswitching operation in the paralleled power supplies to coordinate theAC output current.

By using the internet or ethernet local area network, the set of weldparameters for each power supply is available on a less accurateinformation network, to which the controllers for the paralleled powersupplies are interconnected with a high accuracy digital interface card.Thus, the switching of the individual, paralleled power supplies of thesystem is coordinated. This is an advantage allowing use of the internetand local area network control of a welding system. The informationnetwork includes synchronizing signals for initiating several arcwelding systems connected to several electrodes in a tandem weldingoperation in a selected phase relationship. Each of the welding systemsof an electrode has individual switch points accurately controlled whilethe systems are shifted or delayed to prevent magnetic interferencebetween different electrodes. This allows driving of several ACelectrodes using a common information network. The Houston U.S. Pat. No.6,472,634 system is especially useful for paralleled power supplies topower a given electrode with AC current. The switch points arecoordinated by an accurate interface and the weld parameter for eachparalleled power supply is provided by the general information network.This background is technology developed and patented by assignee anddoes not necessarily constitute prior art just because it is herein usedas “background.”

As a feature of the system in Stava U.S. Pat. No. 6,207,929, two or morepower supplies can drive a single electrode. Thus, the system comprisesa first controller for a first power supply to cause the first powersupply to create an AC current between the electrode and workpiece bygenerating a switch signal with polarity reversing switching points ingeneral timed relationship with respect to a given system synchronizingsignal received by the first controller. This first controller isoperated at first welding parameters in response to a set of first powersupply specific parameter signals directed to the first controller.There is provided at least one slave controller for operating the slavepower supply to create an AC current between the same electrode andworkpiece by reversing polarity of the AC current at switching points.The slave controller operates at second weld parameters in response tothe second set of power supply specific parameter signals to the slavecontroller. An information network connected to the first controller andthe second or slave controller contains digital first and second powersupply specific parameter signals for the two controllers and the systemspecific synchronizing signal. Thus, the controllers receive theparameter signals and the synchronizing signal from the informationnetwork, which may be an ethernet network with or without an internetlink, or merely a local area network. The invention involves a digitalinterface connecting the first controller and the slave controller tocontrol the switching points of the second or slave power supply by theswitch signal from the first or master controller. In practice, thefirst controller starts a current reversal at a switch point. This eventis transmitted at high accuracy to the slave controller to start itscurrent reversal process. When each controller senses an arc currentless than a given number, a “ready signal” is created. After a “ready”signal from all paralleled power supplies, all power supplies reversepolarity. This occurs upon receipt of a strobe or look command each 25μs. Thus, the switching is in unison and has a delay of less than 25 μs.Consequently, both of the controllers have interconnected datacontrolling the switching points of the AC current to the singleelectrode. The same controllers receive parameter information and asynchronizing signal from an information network which in practicecomprises a combination of internet and ethernet or a local areaethernet network. The timing accuracy of the digital interface is lessthan about 10 μs and, preferably, in the general range of 1–5 μs. Thus,the switching points for the two controllers driving a single electrodeare commanded within less than 5 μs. Then, switching actually occurswithin 25 μs. At the same time, relatively less time sensitiveinformation is received from the information network also connected tothe two controllers driving the AC current to a single electrode in atandem welding operation. The 25 μs maximum delay can be changed, but isless than the switch command accuracy.

The unique control system disclosed in Houston U.S. Pat. No. 6,472,634is used to control the power supply for tandem electrodes used primarilyin pipe seam welding and disclosed in Stava U.S. Pat. No. 6,291,798.This Stava patent relates to a series of tandem electrodes movable alonga welding path to lay successive welding beads in the space between theedges of a rolled pipe or the ends of two adjacent pipe sections. Theindividual AC waveforms used in this unique technology are created by anumber of current pulses occurring at a frequency of at least 18 kHzwith a magnitude of each current pulse controlled by a wave shaper. Thistechnology dates back to Blankenship U.S. Pat. No. 5,278,390. Shaping ofthe waveforms in the AC currents of two adjacent tandem electrodes isknown and is shown in not only the patents mentioned above, but in StavaU.S. Pat. No. 6,207,929. In this latter Stava patent, the frequency ofthe AC current at adjacent tandem electrodes is adjusted to preventmagnetic interference. All of these patented technologies by The LincolnElectric Company of Cleveland, Ohio have been advances in the operationof tandem electrodes each of which is operated by a separate AC waveformcreated by the waveform technology set forth in these patents. Thesepatents are incorporated by reference herein. However, these patents donot disclose the present invention which is directed to the use of suchwaveform technology for use in tandem welding by adjacent electrodeseach using an AC current. This technology, as the normal transformertechnology, has experienced difficulty in controlling the dynamics ofthe weld puddle. Thus, there is a need for an electric arc weldingsystem for adjacent tandem electrodes which is specifically designed tocontrol the dynamics and physics of the molten weld puddle during thewelding operation. These advantages can not be obtained by merelychanging the frequency to reduce the magnetic interference.

To control penetration by the lead electrode in tandem electric arcwelding or welding system, a unique leading electrode arrangement hasbeen used for a number of years. The initial concept involved two movinglead electrodes connected to the power source in a series so currentwould flow from the tip of one electrode to the tip of the adjacentelectrode. Both of these electrodes were movable toward a common pointat the weld puddle in the groove between the edges of the workpiecebeing welded. By using a series arrangement, one electrode was connectedto the work terminal of the power source and the other was connected tothe normal electrode terminal. All of the power was between theelectrodes and not between the electrode and the workpiece.Consequently, there was essentially zero arc force. The electrodes weremelted by the current flow between the electrodes. This provided adouble deposition rate with a substantially reduced heat input to theweld puddle. The heat to the puddle was, thus, decreased. Thedisadvantage of the series electrode concept was that there was verylittle penetration. The arc did not extend to the workpiece. The metalwas deposited into the joint between the edges of the workpieceprimarily by gravity. To increase the penetration of the lead arc by thetwo series electrodes, the trailing electrode was also connected tomachine ground. This concept is disclosed in Shutt U.S. Pat. No.4,246,463. In this arrangement, the arc traveled between the twoelectrodes and from the lead electrode to the workpiece. With two 3/16inch electrodes, the modified series arc system had the current from thelead electrode flowing through two paths back to the power source. Thecurrent either passed to the trailing electrode or to the workpiece. Inpractice, the ratio of current flow from the lead electrode back to thepower source is approximately ⅓ through the work and ⅔ through theelectrode. The work had substantially more resistance in the returnparallel circuit. This arrangement doubled the deposition rate. Theamount of current into the plate or workpiece was about 30% of the totalcurrent of the welding operation. Consequently, there was doubledeposition rate and decreased heat into the plate. Penetration wascaused by the modified series circuit connection of the two leadelectrodes. This single side welding of heavy workpieces has not beenused extensively because the frequency of the AC current in the seriesconnected electrodes was controlled by the line frequency of the powersource. The wire feeder for each of the electrodes was controlled by thesame power source. This limited the relationship of the two motorsdriving the wire feeders. The input voltage and frequency of the powersource was used to drive both wire feeders. Consequently, using theprior art system with all of its apparent advantages could beaccomplished in only a relatively small range of currents and with onlycertain limited electrode sizes. Thus, using the prior art system wasrestricted. There had to be a tuning of the current and input frequencyfor proper melting, penetration and wire feed speed. The parameters ofthe power source and the interrelationship of the two independentlydriven wire feeders rendered the advantageous prior welding technique ofa tandem arc welder where the two electrodes are connected in series anddriven by AC current to be quite limited. Since there is a limitedapplication of this technology, it was not possible to sell seriesconnected tandem electrode equipment for general purpose electric arcwelding. Consequently, the advantages of modified series connectedelectrodes in a tandem welding system has essentially lay dormantthrough the many years of its existence.

THE INVENTION

To render universally acceptable and usable, a tandem electric arcwelder or system having two lead electrodes connected in a modifiedseries circuit, the present invention was developed. By using thepresent invention, large plates can be welded from one side in asubmerged arc welding operation, with an arc force causing penetrationwhile the series connected electrodes substantially increase thedeposition. By using the present invention, a root weld bead isdeposited by the two series connected lead electrodes. This tacks thetwo spaced edges of the workpiece together. In practice the large platesare ship sheet plates or the ends of pipe segments in pipe welding. Thisinvention modifies the well known series connected lead electrodeconcept for tandem welding so that such a welder can be used with alarge variety of currents and a large variety of electrodes, both sizeand material. This is a substantial advance in the electric arc weldingfield and solves the reason for the lack of use of the modified seriesconnected tandem electrodes in one side, submerged arc welding. Themodification can be used in other types of welding.

In accordance with the present invention, there is provided an electricarc welder for depositing weld metal along the groove between edges of ametal workpiece. The welder comprises an electrode driven by the wirefeeder toward a point in the groove. A second electrode is driven by asecond wire feeder toward the same point in the groove. A main powersource is connected to the electrode with a first output terminal of thepower source connected to the first electrode and a second outputterminal of the main power source connected to both the second electrodeand directly or indirectly to the metal workpiece. The welder includestwo return paths, one through the second electrode and one through theworkpiece. The power source includes a high speed switching output stagesuch as an inverter chopper. This stage creates current with a selectedAC waveform between the first and second output terminals of the mainpower source. The waveform of the main power source is generated by awaveform generator controlling a pulse width modulator circuit normallya digital circuit, but in some instances it is an analog PWM circuit.The pulse width modulator circuit, digital or analog, determines thecurrent operation of the output stage of the main power source. A deviceis used to move the electrodes in unison along the groove in a givendirection. These electrodes form the lead electrodes in a tandemelectrode arc welder or electric arc welding system. In accordance withthe preferred embodiment of the present invention, a third, fourth orfifth electrode is connected behind the first and second seriesconnected electrodes. Each of these following electrodes is movable withthe first series connected electrodes. In practice, they are movable onthe same mechanism or tractor; however, they could be moved separatelyand still be “generally movable” with the first and second seriesconnected electrodes. The third or subsequent electrodes are eachpowered by an auxiliary power source different from the main powersource, with the first output terminal connected to the third electrodeand a second output terminal connected to the workpiece. This is astandard connection for the trailing electrodes of a tandem weldingoperation.

Still a further aspect of the present invention is the provision of anelectric arc welder as defined above wherein the auxiliary power sourcefor the tailing electrodes also includes a high speed switching outputstage, such as an inverter or chopper. This output stage creates aselected trailing waveform between the first and second output terminalsof the auxiliary power source. The trailing waveform of the auxiliarypower source is generated by a waveform generator controlling the pulsewidth modulator circuit, either digital or analog, to determine thecurrent operation of the output stage of the auxiliary power source. Thenumber of power sources, as shown in the prior art, can vary accordingto the number of trailing electrodes. Indeed, one power source canoperate two trailing electrodes or two power sources can operate asingle trailing electrode. These are all variations used in tandemelectric arc welding as defined in the various patents incorporated byreference herein.

In accordance with an aspect of the invention, the trailing waveforms ofthe trailing electrodes are also an AC waveform, such as used in theseries connected lead electrodes of the electric welder constructed inaccordance with the present invention. Of course, the trailingelectrodes could have waveforms which are DC waveforms created by thewaveform generator producing a steady output signal for determining themagnitude of the DC waveform. In this instance, waveform is a level ofcurrent, whereas “waveform” is used in this application primarily tomean a repeating AC waveform.

In accordance with a more limited aspect of the present invention, themain power source includes a first and second module power sourceconnected in parallel with the output terminals of the main powersource. To provide greater current, a second module is connected inparallel with a first module. The two power source modules are definedas the “main” power source driving the series connected lead electrodesof the present invention. In the preferred implementation, a secondpower source is connected in series between the second electrode and theworkpiece. In this arrangement, one terminal of the main power sourceand a terminal of the second power source are connected in series and tothe second electrode. The second power source is in the workpiece path.By using two power sources, the separate independently driven wirefeeders for the two series connected electrodes can be controlled bydifferent power sources. This prevents a complicated softwaredevelopment when a single power source is used to drive the separate twowire feeders used for the lead electrodes of the invention.Consequently, there is an advantage of using two separate power sources,with each of the power sources having a wire feed control circuit thatcan be adjusted to optimize the wire feeder of each of the seriesconnected electrodes forming the lead electrodes of the tandem weldingsystem obtained by the present invention.

The present invention is primarily used for one sided welding on largeplates. In this context, the invention also includes the concept of aback plate below the groove accepting the weld metal. The back plate ison the underside of the workpiece and normally provides a trough withflux that controls the backside weld bead configuration. In accordancewith an aspect, there is a flux dispenser in front of the trailingelectrodes. Thus, the trailing electrodes are used for submerged arcwelding. In practice, the first series electrodes are either gasshielded or provided with a flux dispenser to create a submerged arcwelding process for the first two electrodes.

By using the present invention, the waveform generator for the mainpower source is provided with a circuit to adjust the frequency of theAC waveform between the series connected lead electrodes. In thismanner, the frequency of the AC waveform used in the series connectedelectrodes is not dictated in any fashion by the frequency of linevoltage to the main power source. By adjusting the frequency of thewaveform, the welding operation for the series connected electrodes canbe modulated to accommodate different diameter electrodes, electrodeswith different material and a variety of currents to customize thewelding operation in a manner not available in the prior art.Furthermore, the waveform generator of the present invention has acircuit for adjusting duty cycles of the AC waveforms from the mainpower source. Thus, the welding operation can be adjusted betweenpenetration and deposition to customize the operation of the weldprocess. To accomplish this objective, the magnitude of the positivecurrent portion of the waveform are controlled independently or as apercentage of the magnitude of the negative portion of the AC waveform.All of these adjustment circuits allow the main power source to beadjusted in frequency, duty cycle and/or amplitudes to customize thewelder for providing an optimized welding process, while still employingthe tremendously advantageous series connected electrodes.

The primary object of the present invention is the provision of a tandemelectric arc welder wherein the lead electrodes are connected in series,which welder includes an AC current waveform in the two series connectedelectrodes, which waveform can be adjusted to customize the weldingoperation performed by the lead electrodes in the tandem electrodewelder.

Another object of the present invention is the provision of an electricarc welder, as defined above, which electric arc welder can usedifferent electrodes and different current settings to perform the ACarc welding process with the series connected lead electrodes.

Yet another object of the present invention is the provision of anelectric arc welder, as defined above, which electric arc welder has thecapabilities of adjusting the frequency of the waveform, the duty cycleof the waveform and/or the magnitude of the current in the positive andnegative portions of the waveform so that the welding process performedby the lead series connected electrodes are customized.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a welder used to practice the presentinvention;

FIG. 2 is a wiring diagram of two paralleled power supplies, each ofwhich include a switching output which power supplies;

FIG. 3 is a cross sectional side view of three tandem electrodes forwelding the seam of a pipe;

FIG. 4 is a schematic layout in block form of a welding system for threeelectrodes using the disclosure in Houston U.S. Pat. No. 6,472,634 andStava U.S. Pat. No. 6,291,798;

FIG. 5 is a block diagram showing a single electrode driven by thesystem as shown in FIG. 4 with a variable pulse generator disclosed inHouston U.S. Pat. No. 6,472,634;

FIG. 6 is a current graph for one of two illustrated synchronizingpulses and showing a balanced AC waveform for one tandem electrode;

FIG. 7 is a current graph superimposed upon a signal having logic todetermine the polarity of the waveform as used in practicing the presentinvention;

FIG. 8 is a current graph showing a broad aspect of waveforms used inthe preferred embodiment of the present invention;

FIGS. 9 and 10 are schematic drawings illustrating the dynamics of theweld puddle during concurrent polarity relationships of tandemelectrodes;

FIG. 11 is a pair of current graphs showing the waveforms on twoadjacent tandem electrodes;

FIG. 12 is a pair of current graphs of the AC waveforms on adjacenttandem electrodes with areas of concurring polarity relationships;

FIG. 13 are current graphs of the waveforms on adjacent tandemelectrodes wherein the AC waveform of one electrode is substantiallydifferent waveform of the other electrode to limit the time ofconcurrent polarity relationships;

FIG. 14 are current graphs of two sinusoidal waveforms for adjacentelectrodes to use different shaped wave forms for the adjacent tandemelectrodes;

FIG. 15 are current graphs showing waveforms at four adjacent AC arcs oftandem electrodes shaped and synchronized in accordance with the welderconstructed in accordance with the invention;

FIG. 16 is a schematic layout of the software program to cause switchingof the paralleled power supplies as soon as the coordinated switchcommands have been processed and the next coincident signal has beencreated;

FIG. 17 is a schematic view of the general architecture of the preferredembodiment of the present invention;

FIG. 18 is a partial cross-sectional view taken generally along line18—18 of FIG. 17;

FIG. 19 is a schematic layout of the software program, together with ablock diagram schematically illustrating the operation of the main powersource used in the preferred embodiment of the present invention;

FIG. 20 is a partial side elevational view of the preferred embodimentof the present invention illustrating only the lead series connectedelectrode used in the present invention with a modification of the mainpower source; and,

FIG. 21 is a view similar to FIG. 20 showing the preferred embodimentand practical embodiment now used for the main power source and theworkpiece path of the present invention.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and not forthe purpose of limiting same, the system used in practicing theinvention is shown in detail in FIGS. 1, 2 and 16. In FIG. 1 there is asingle electric arc welding system S in the form of a single cell tocreate an alternating current as an arc at weld station WS. This systemor cell includes a first master welder A with output leads 10, 12 inseries with electrode E and workpiece W in the form of a pipe seam jointor other welding operation. Hall effect current transducer 14 provides avoltage in line 16 proportional to the current of welder A. Less timecritical data, such as welding parameters, are generated at a remotecentral control 18. In a like manner, a slave following welder Bincludes leads 20, 22 connected in parallel with leads 10, 12 to directan additional AC current to the weld station WS. Hall effect currenttransducer 24 creates a voltage in line 26 representing current levelsin welder B during the welding operation. Even though a single slave orfollower welder B is shown, any number of additional welders can beconnected in parallel with master welder A to produce an alternatingcurrent across electrode E and workpiece W. The AC current is combinedat the weld station instead of prior to a polarity switching network.Each welder includes a controller and inverter based power supplyillustrated as a combined master controller and power supply 30 and aslave controller and power supply 32. Controllers 30,32 receiveparameter data and synchronization data from a relatively low levellogic network. The parameter information or data is power supplyspecific whereby each of the power supplies is provided with the desiredparameters such as current, voltage and/or wire feed speed. A low leveldigital network can provide the parameter information; however, the ACcurrent for polarity reversal occurs at the same time. The “same” timeindicates a time difference of less than 10 μs and preferably in thegeneral range of 1–5 μs. To accomplish precise coordination of the ACoutput from power supply 30 and power supply 32, the switching pointsand polarity information can not be provided from a general logicnetwork wherein the timing is less precise. The individual AC powersupplies are coordinated by high speed, highly accurate DC logicinterface referred to as “gateways.” As shown in FIG. 1, power supplies30, 32 are provided with the necessary operating parameters indicated bythe bi-directional leads 42 m, 42 s, respectively. This non-timesensitive information is provided by a digital network shown in FIG. 1.Master power supply 30 receives a synchronizing signal as indicated byunidirectional line 40 to time the controllers operation of its ACoutput current. The polarity of the AC current for power supply 30 isoutputted as indicated by line 46. The actual switching command for theAC current of master power supply 30 is outputted on line 44. The switchcommand tells power supply S, in the form of an inverter, to “kill,”which is a drastic reduction of current. In an alternative, this isactually a switch signal to reverse polarity. The “switching points” orcommand on line 44 preferably is a “kill” and current reversal commandsutilizing the “switching points” as set forth in Stava U.S. Pat. No.6,111,216. Thus, timed switching points or commands are outputted frompower supply 30 by line 44. These switching points or commands mayinvolve a power supply “kill” followed by a switch ready signal at a lowcurrent or merely a current reversal point. The switch “ready” is usedwhen the “kill” concept is implemented because neither inverters are toactually reverse until they are below the set current. This is describedin FIG. 16. The polarity of the switches of controller 30 controls thelogic on line 46. Slave power supply 32 receives the switching point orcommand logic on line 44 b and the polarity logic on line 46 b. Thesetwo logic signals are interconnected between the master power supply andthe slave power supply through the highly accurate logic interface shownas gateway 50, the transmitting gateway, and gateway 52, the receivinggateway on lines 44 a, 46 a. These gateways are network interface cardsfor each of the power supplies so that the logic on lines 44 b, 46 b aretimed closely to the logic on lines 44, 46, respectively. In practice,network interface cards or gateways 50, 52 control this logic to within10 μs and preferably within 1–5 μs. A low accuracy network controls theindividual power supplies for data from central control 18 through lines42 m, 42 s, illustrated as provided by the gateways or interface cards.These lines contain data from remote areas (such as central control 18)which are not time sensitive and do not use the accuracy characteristicsof the gateways. The highly accurate data for timing the switch reversaluses interconnecting logic signals through network interface cards 50,52. The system in FIG. 1 is a single cell for a single AC arc; however,the invention is directed to tandem electrodes wherein two or more ACarcs are created to fill the large gap found in pipe welding. Thus, themaster power supply 30 for the first electrode receives asynchronization signal which determines the timing or phase operation ofthe system S for a first electrode, i.e. ARC 1. System S is used withother identical systems to generate ARCs 2, 3, and 4 timed bysynchronizing outputs 84, 86 and 88. This concept is schematicallyillustrated in FIG. 5. The synchronizing or phase setting signals 82–88are shown in FIG. 1 with only one of the tandem electrodes. Aninformation network N comprising a central control computer and/or webserver 60 provides digital information or data relating to specificpower supplies in several systems or cells controlling differentelectrodes in a tandem operation. Internet information 62 is directed toa local area network in the form of an ethernet network 70 having localinterconnecting lines 70 a, 70 b, 70 c. Similar interconnecting linesare directed to each power supply used in the four cells creating ARCs1, 2, 3 and 4 of a tandem welding operation. The description of systemor cell S applies to each of the arcs at the other electrodes. If ACcurrent is employed, a master power supply is used. In some instances,merely a master power supply is used with a cell specific synchronizingsignal. If higher currents are required, the systems or cells include amaster and slave power supply combination as described with respect tosystem S of FIG. 1. In some instances, a DC arc is used with two or moreAC arcs synchronized by generator 80. Often the DC arc is the leadingelectrode in a tandem electrode welding operation, followed by two ormore synchronized AC arcs. A DC power supply need not be synchronized,nor is there a need for accurate interconnection of the polarity logicand switching points or commands. Some DC powered electrodes maybeswitched between positive and negative, but not at the frequency of anAC driven electrode. Irrespective of the make-up of the arcs, ethernetor local area network 70 includes the parameter information identifiedin a coded fashion designated for specific power supplies of the varioussystems used in the tandem welding operation. This network also employssynchronizing signals for the several cells or systems whereby thesystems can be offset in a time relationship. These synchronizingsignals are decoded and received by a master power supply as indicatedby line 40 in FIG. 1. In this manner, the AC arcs are offset on a timebasis. These synchronizing signals are not required to be as accurate asthe switching points through network interface cards or gateways 50, 52.Synchronizing signals on the data network are received by a networkinterface in the form of a variable pulse generator 80. The generatorcreates offset synchronizing signals in lines 84, 86 and 88. Thesesynchronizing signals dictate the phase of the individual alternatingcurrent cells for separate electrodes in the tandem operation.Synchronizing signals can be generated by interface 80 or actuallyreceived by the generator through the network 70. In practice, network70 merely activates generator 80 to create the delay pattern for themany synchronizing signals. Also, generator 80 can vary the frequency ofthe individual cells by frequency of the synchronizing pulses if thatfeature is desired in the tandem welding operation.

A variety of controllers and power supplies could be used for practicingthe system as described in FIG. 1; however, preferred implementation ofthe system is set forth in FIG. 2 wherein power supply PSA is combinedwith controller and power supply 30 and power supply PSB is combinedwith controller and power supply 32. These two units are essentially thesame in structure and are labeled with the same numbers whenappropriate. Description of power supply PSA applies equally to powersupply PSB. Inverter 100 has an input rectifier 102 for receiving threephase line current L1, L2, and L3. Output transformer 110 is connectedthrough an output rectifier 112 to tapped inductor 120 for drivingopposite polarity switches Q1, Q2. Controller 140 a of power supply PSAand controller 140 b of PSB are essentially the same, except controller140 a outputs timing information to controller 140 b. Switching pointsor lines 142, 144 control the conductive condition of polarity switchesQ1, Q2 for reversing polarity at the time indicated by the logic onlines 142, 144, as explained in more detail in Stava U.S. Pat. No.6,111,216 incorporated by reference herein. The control is digital witha logic processor; thus, A/D converter 150 converts the currentinformation on feedback line 16 or line 26 to controlling digital valuesfor the level of output from error amplifier 152 which is illustrated asan analog error amplifier. In practice, this is a digital system andthere is no further analog signal in the control architecture. Asillustrated, however, amplifier has a first input 152 a from converter150 and a second input 152 b from controller 140 a or 140 b. The currentcommand signal on line 152 b includes the wave shape or waveformrequired for the AC current across the arc at weld station WS. This isstandard practice as taught by several patents of Lincoln Electric, suchas Blankenship U.S. Pat. No. 5,278,390, incorporated by reference. Seealso Stava U.S. Pat. No. 6,207,929, incorporated by reference. Theoutput from amplifier 152 is converted to an analog voltage signal byconverter 160 to drive pulse width modulator 162 at a frequencycontrolled by oscillator 164, which is a timer program in the processorsoftware. The shape of the waveform at the arcs is the voltage ordigital number at lines 152 b. The frequency of oscillator 164 isgreater than 18 kHz. The total architecture of this system is digitizedin the preferred embodiment of the present invention and does notinclude reconversion back into analog signal. This representation isschematic for illustrative purposes and is not intended to be limitingof the type of power supply used in practicing the present invention.Other power supplies could be employed.

The practice of the present invention utilizing the concepts of FIGS. 1and 2 are illustrated in FIGS. 3 and 4. Workpiece 200 is a seam in apipe which is welded together by tandem electrodes 202, 204 and 206powered by individual power supplies PS1, PS2, PS3, respectively. Thepower supplies can include more than one power source coordinated inaccordance with the technology in Houston U.S. Pat. No. 6,472,634. Theillustrated embodiment involves a DC arc for lead electrode 202 and anAC arc for each of the tandem electrodes 204, 206. The created waveformsof the tandem electrodes are AC currents and include shapes created by awave shaper or wave generator in accordance with the previouslydescribed waveform technology. As electrodes 202, 204 and 206 are movedalong weld path WP a molten metal puddle P is deposited in pipe seam 200with an open root portion 210 followed by deposits 212, 214 and 216 fromelectrodes 202, 204 and 206, respectively. As previously described morethan two AC driven electrodes as will be described and illustrated bythe waveforms of FIG. 15, can be operated by the invention relating toAC currents of adjacent electrodes. The power supplies, as shown in FIG.4, each include an inverter 220 receiving a DC link from rectifier 222.In accordance with Lincoln waveform technology, a chip or internalprogrammed pulse width modulator stage 224 is driven by an oscillator226 at a frequency greater than 18 kHz and preferably greater than 20kHz. As oscillator 226 drives pulse width modulator 224, the outputcurrent has a shape dictated by the wave shape outputted from waveshaper 240 as a voltage or digital numbers at line 242. Output leads217, 218 are in series with electrodes 202, 204 and 206. The shape inreal time is compared with the actual arc current in line 232 from HallEffect transducer 228 by a stage illustrated as comparator 230 so thatthe outputs on line 234 controls the shape of the AC waveforms. Thedigital number or voltage on line 234 determines the output signal online 224 a to control inverter 220 so that the waveform of the currentat the arc follows the selected profile outputted from wave shaper 240.This is standard Lincoln waveform technology, as previously discussed.Power supply PS1 creates a DC arc at lead electrode 202; therefore, theoutput from wave shaper 240 of this power supply is a steady stateindicating the magnitude of the DC current. The present invention doesnot relate to the formation of a DC arc. To the contrary, the presentinvention is the control of the current at two adjacent AC arcs fortandem electrodes, such as electrodes 204, 206. In accordance with theinvention, wave shaper 240 involves an input 250 employed to select thedesired shape or profile of the AC waveform. This shape can be shiftedin real time by an internal programming schematically represented asshift program 252. Wave shaper 240 has an output which is a prioritysignal on line 254. In practice, the priority signal is a bit of logic,as shown in FIG. 7. Logic 1 indicates a negative polarity for thewaveform generated by wave shaper 240 and logic 0 indicates a positivepolarity. This logic signal or bit controller 220 directed to the powersupply is read in accordance with the technology discussed in FIG. 16.The inverter switches from a positive polarity to a negative polarity,or the reverse, at a specific “READY” time initiated by a change of thelogic bit on line 254. In practice, this bit is received from variablepulse generator 80 shown in FIG. 1 and in FIG. 5. The welding systemshown in FIGS. 3 and 4 is used in practicing the invention wherein theshape of AC arc currents at electrodes 204 and 206 have novel shapes toobtain a beneficial result of the present invention, i.e. a generallyquiescent molten metal puddle P and/or synthesized sinusoidal waveformscompatible with transformer waveforms used in arc welding. The electricarc welding system shown in FIGS. 3 and 4 have a program to select thewaveform at “SELECT” program 250 for wave shaper 240. In this manner theunique waveforms of the present invention are used by the tandemelectrodes. One of the power supplies to create an AC arc isschematically illustrated in FIG. 5. The power supply or source iscontrolled by variable pulse generator 80, shown in FIG. 1. Signal 260from the generator controls the power supply for the first arc. Thissignal includes the synchronization of the waveform together with thepolarity bit outputted by the wave shaper 240 on line 254. Lines 260a–260 n control the desired subsequent tandem AC arcs operated by thewelding system of the present invention. The timing of these signalsshifts the start of the other waveforms. FIG. 5 merely shows therelationship of variable pulse generator 80 to control the successivearcs as explained in connection with FIG. 4.

In the welding system of Houston U.S. Pat. No. 6,472,634, the ACwaveforms are created as shown in FIG. 6 wherein the wave shaper for arcAC1 at electrode 204 creates a signal 270 having positive portions 272and negative portions 274. The second arc AC2 at electrode 206 iscontrolled by signal 280 from the wave shaper having positive portions282 and negative portions 284. These two signals are the same, but areshifted by the signal from generator 80 a distance x, as shown in FIG.6. The waveform technology created current pulses or waveforms at one ofthe arcs are waveforms having positive portions 290 and negativeportions 292 shown at the bottom portion of FIG. 6. A logic bit from thewave shaper determines when the waveform is switched from the positivepolarity to the negative polarity and the reverse. In accordance withthe disclosure in Stava U.S. Pat. No. 6,111,216 (incorporated byreference herein) pulse width modulator 224 is generally shifted to alower level at point 291 a and 291 b. Then the current reduces untilreaching a fixed level, such as 100 amps. Consequently, the switcheschange polarity at points 294 a and 294 b. This produces a vertical lineor shape 296 a, 296 b when current transitioning between positiveportion 290 and negative portion 292. This is the system disclosed inthe Houston patent where the like waveforms are shifted to avoidmagnetic interference. The waveform portions 290, 292 are the same atarc AC1 and at arc AC2. This is different from the present inventionwhich relates to customizing the waveforms at arc AC1 and arc AC2 forpurposes of controlling the molten metal puddle and/or synthesizing asinusoidal wave shape in a manner not heretofore employed. Thedisclosure of FIG. 6 is set forth to show the concept of shifting thewaveforms, but not the invention which is customizing each of theadjacent waveforms. The same switching procedure to create a verticaltransition between polarities is used in the preferred embodiment of thepresent invention. Converting from the welding system shown in FIG. 6 tothe present invention is generally shown in FIG. 7. The logic on line254 is illustrated as being a logic 1 in portions 300 and a logic 0 inportions 302. The change of the logic or bit numbers signals the timewhen the system illustrated in FIG. 16 shifts polarity. This isschematically illustrated in the lower graph of FIG. 6 at points 294 a,294 b. In accordance with the invention, wave shaper 240 for each of theadjacent AC arcs has a first wave shape 310 for one of the polaritiesand a second wave shape 312 for the other polarity. Each of thewaveforms 310, 312 are created by the logic on line 234 taken togetherwith the logic on line 254. Thus, pulses 310, 312 as shown in FIG. 7,are different pulses for the positive and negative polarity portions.Each of the pulses 310, 312 are created by separate and distinct currentpulses 310 a, 312 a as shown. Switching between polarities isaccomplished as illustrated in FIG. 6 where the waveforms generated bythe wave shaper are shown as having the general shape of waveforms 310,312. Positive polarity controls penetration and negative polaritycontrols deposition. In accordance with the invention, the positive andnegative pulses of a waveform are different and the switching points arecontrolled so that the AC waveform at one arc is controlled both in thenegative polarity and the positive polarity to have a specific shapecreated by the output of wave shaper 240. The waveforms for the arcadjacent to the arc having the current shown in FIG. 7 is controlleddifferently to obtain the advantages of the present invention. This isillustrated best in FIG. 8. The waveform at arc AC 1 is in the top partof FIG. 8. It has positive portions 320 shown by current pulses 320 aand negative portions 322 formed by pulses 322 a. Positive portion 320has a maximum magnitude a and width or time period b. Negative portion322 has a maximum magnitude d and a time or period c. These fourparameters are adjusted by wave shaper 240. In the illustratedembodiment, arc AC2 has the waveform shown at the bottom of FIG. 8 wherepositive portion 330 is formed by current pulses 330 a and has a heightor magnitude a′ and a time length or period b′. Negative portion 332 isformed by pulses 332 a and has a maximum amplitude b′ and a time lengthc′. These parameters are adjusted by wave shaper 240. In accordance withthe invention, the waveform from the wave shaper on arc AC1 is out ofphase with the wave shape for arc AC2. The two waveforms have parametersor dimensions which are adjusted so that (a) penetration and depositionis controlled and (b) there is no long time during which the puddle P issubjected to a specific polarity relationship, be it a like polarity oropposite polarity. This concept in formulating the wave shapes preventslong term polarity relationships as explained by the showings in FIGS. 9and 10. In FIG. 9 electrodes 204, 206 have like polarity, determined bythe waveforms of the adjacent currents at any given time. At thatinstance, magnetic flux 350 of electrode 204 and magnetic flux 352 ofelectrode 206 are in the same direction and cancel each other at centerarea 354 between the electrodes. This causes the molten metal portions360, 362 from electrodes 204, 206 in the molten puddle P to movetogether, as represented by arrows c. This inward movement together orcollapse of the molten metal in puddle P between electrodes 204 willultimately cause an upward gushing action, if not terminated in a veryshort time, i.e. less than about 20 ms. As shown in FIG. 10, theopposite movement of the puddle occurs when the electrodes 204, 206 haveopposite polarities. Then, magnetic flux 370 and magnetic flux 372 areaccumulated and increased in center portion 374 between the electrodes.High forces between the electrodes causes the molten metal portions 364,366 of puddle P to retract or be forced away from each other. This isindicated by arrows r. Such outward forcing of the molten metal inpuddle P causes disruption of the weld bead if it continues for asubstantial time which is generally less than 10 ms. As can be seen fromFIGS. 9 and 10, it is desirable to limit the time during which thepolarity of the waveform at adjacent electrodes is either the samepolarity or opposite polarity. As shown in FIG. 8, like polarity andopposite polarity is retained for a very short time less than the cyclelength of the waveforms at arc AC1 and arc AC2. This positivedevelopment of preventing long term occurrence of polarity relationshipstogether with the novel concept of pulses having different shapes anddifferent proportions in the positive and negative areas combine tocontrol the puddle, control penetration and control deposition in amanner not heretofore obtainable in welding with a normal transformerpower supplies or normal use of Lincoln waveform technology.

In FIG. 11 the positive and negative portions of the AC waveform fromthe wave shaper 240 are synthesized sinusoidal shapes with a differentenergy in the positive portion as compared to the negative portion ofthe waveforms. The synthesized sine wave or sinusoidal portions of thewaveforms is novel. It allows the waveforms to be compatible withtransformer welding circuits and compatible with evaluation of sine wavewelding. In FIG. 11, waveform 370 is at arc AC1 and waveform 372 is atarc AC2. These tandem arcs utilize the AC welding current shown in FIG.11 wherein a small positive sinusoidal portion 370 a controlspenetration at arc AC1 while the larger negative portion 370 b controlsthe deposition of metal at arc AC1. There is a switching between thepolarities with a change in the logic bit, as discussed in FIG. 7.Sinusoidal waveform 370 plunges vertically from approximately 100amperes through zero current as shown in by vertical line 370 c.Transition between the negative portion 370 b and positive portion 370 aalso starts a vertical transition at the switching point causing avertical transition 370 d. In a like manner, phase shifted waveform 372of arc AC2 has a small penetration portion 372 a and a large negativedeposition portion 372 b. Transition between polarities is indicated byvertical lines 372 c and 372 d. Waveform 372 is shifted with respect towaveform 370 so that the dynamics of the puddle are controlled withoutexcessive collapsing or repulsion of the molten metal in the puddlecaused by polarities of adjacent arcs AC1, AC2. In the embodiment shownin FIG. 11, the sine wave shapes are the same and the frequencies arethe same. They are merely shifted to prevent a long term occurrence of aspecific polarity relationship.

In FIG. 12 waveform 380 is used for arc AC1 and waveform 382 is used forarc AC2. Portions 380 a, 380 b, 382 a, and 382 b are sinusoidalsynthesized and are illustrated as being of the same general magnitude.By shifting these two waveforms 90°, areas of concurrent polarity areidentified as areas 390, 392, 394 and 396. By using the shiftedwaveforms with sinusoidal profiles, like polarities or oppositepolarities do not remain for any length of time. Thus, the molten metalpuddle is not agitated and remains quiescent. This advantage of theconcept of a difference in energy between the positive and negativepolarity portions of a given waveform. FIG. 12 is illustrative in natureto show the definition of concurrent polarity relationships and the factthat they should remain for only a short period of time. To accomplishthis objective, another embodiment of the present invention isillustrated in FIG. 13 wherein previously defined waveform 380 iscombined with waveform 400, shown as the sawtooth waveform of arc AC2(a)or the pulsating waveform 402 shown as the waveform for arc AC2(b).Combining waveform 380 with the different waveform 400 of a differentwaveform 402 produces very small areas or times of concurrent polarityrelationships 410, 412, 414, etc. In FIG. 14 the AC waveform generatedat one arc drastically different than the AC waveform generated at theother arc. This same concept of drastically different waveforms isillustrated in FIG. 14 wherein waveform 420 is an AC pulse profilewaveform and waveform 430 is a sinusoidal profile waveform having aboutone-half the period of waveform 420. Waveform 420 includes a smallpenetration positive portion 420 a and a large deposition portion 420 bwith straight line polarity transitions 420 c. Waveform 430 includespositive portion 430 a and negative portion 430 b with vertical polaritytransitions 430 c. By having these two different waveforms, both thesynthesized sinusoidal concept is employed for one electrode and thereis no long term concurrent polarity relationship. Thus, the molten metalin puddle P remains somewhat quiescent during the welding operation byboth arcs AC1, AC2.

In FIG. 15 waveforms 450, 452, 454 and 456 are generated by the waveshaper 240 of the power supply for each of four tandem arcs, arc AC1,arc AC2, arc AC3 and arc AC4. The adjacent arcs are aligned as indicatedby synchronization signal 460 defining when the waveforms correspond andtransition from the negative portion to the positive portion. Thissynchronization signal is created by generator 80 shown in FIG. 1,except the start pulses are aligned. In this embodiment of the inventionfirst waveform 450 has a positive portion 450 a, which is synchronizedwith both the positive and negative portion of the adjacent waveform452, 454 and 456. For instance, positive portion 450 a is synchronizedwith and correlated to positive portion 452 a and negative portion 452 bof waveform 452. In a like manner, the positive portion 452 a ofwaveform 452 is synchronized with and correlated to positive portion 454a and negative portion 454 b of waveform 454. The same relationshipexist between positive portion 454 a and the portions 456 a, 456 b ofwaveform 456. The negative portion 450 b is synchronized with andcorrelated to the two opposite polarity portions of aligned waveform452. The same timing relationship exist between negative portion 452 band waveform 454. In other words, in each adjacent arc one polarityportion of the waveform is correlated to a total waveform of theadjacent arc. In this manner, the collapse and repelling forces ofpuddle P, as discussed in connection with FIGS. 9 and 10, aredynametically controlled. One or more of the positive or negativeportions can be synthesized sinusoidal waves as discussed in connectionwith an aspect of the invention disclosed in FIGS. 11 and 12.

As indicated in FIGS. 1 and 2, when the master controller of switches isto switch, a switch command is issued to master controller 140 a ofpower supply 30. This causes a “kill” signal to be received by themaster so a kill signal and polarity logic is rapidly transmitted to thecontroller of one or more slave power supplies connected in parallelwith a single electrode. If standard AC power supplies are used withlarge snubbers in parallel with the polarity switches, the slavecontroller or controllers are immediately switched within 1–10 μs afterthe master power supply receives the switch command. This is theadvantage of the high accuracy interface cards or gateways. In practice,the actual switching for current reversal of the paralleled powersupplies is not to occur until the output current is below a givenvalue, i.e. about 100 amperes. This allows use of smaller switches.

The implementation of the switching for all power supplies for a singleAC arc uses the delayed switching technique where actual switching canoccur only after all power supplies are below the given low currentlevel. The delay process is accomplished in the software of the digitalprocessor and is illustrated by the schematic layout of FIG. 16. Whenthe controller of master power supply 500 receives a command signal asrepresented by line 502, the power supply starts the switching sequence.The master outputs a logic on line 504 to provide the desired polarityfor switching of the slaves to correspond with polarity switching of themaster. In the commanded switch sequence, the inverter of master powersupply 500 is turned off or down so current to electrode E is decreasedas read by hall effect transducer 510. The switch command in line 502causes an immediate “kill” signal as represented by line 512 to thecontrollers of paralleled slave power supplies 520, 522 providingcurrent to junction 530 as measured by hall effect transducers 532,534.All power supplies are in the switch sequence with inverters turned offor down. Software comparator circuits 550, 552, 554 compare thedecreased current to a given low current referenced by the voltage online 556. As each power supply decreases below the given value, a signalappears in lines 560, 562, and 564 to the input of a sample and holdcircuits 570, 572, and 574, respectively. The circuits are outputted bya strobe signal in line 580 from each of the power supplies. When a setlogic is stored in a circuit 570, 572, and 574, a YES logic appears onlines READY¹, READY², and READY³ at the time of the strobe signal. Thissignal is generated in the power supplies and has a period of 25 μs;however, other high speed strobes could be used. The signals aredirected to controller C of the master power supply, shown in dashedlines in FIG. 16. A software ANDing function represented by AND gate 584has a YES logic output on line 582 when all power supplies are ready toswitch polarity. This output condition is directed to clock enableterminal ECLK of software flip flop 600 having its D terminal providedwith the desired logic of the polarity to be switched as appearing online 504. An oscillator or timer operated at about 1 MHz clocks flipflop by a signal on line 602 to terminal CK. This transfers the polaritycommand logic on line 504 to a Q terminal 604 to provide this logic inline 610 to switch slaves 520, 522 at the same time the identical logicon line 612 switches master power supply 500. After switching, thepolarity logic on line 504 shifts to the opposite polarity while masterpower supply awaits the next switch command based upon the switchingfrequency. Other circuits can be used to effect the delay in theswitching sequence; however, the illustration in FIG. 16 is the presentscheme.

The present application relates to the waveforms controlled by a waveshaper or waveform generator of an electric arc power supply including asingle power source or multiple power sources correlated as disclosed inHouston U.S. Pat. No. 6,472,634 or Stava U.S. Pat. No. 6,291,798. Theinvention relates to tandem electrodes powered by an AC waveform. Thetwo adjacent electrodes have waveforms that control the dynamics of themolten metal puddle between the electrodes and/or uses synthesized sinewaves to correlate the operation of the tandem welding system withstandard transformer welding operations. Different energy in thepositive portion and negative portion controls the relationship of theamount of penetration to the amount of deposition by a particularelectrode. This allows operation of adjacent electrodes in a manner tomaintain the weld puddle generally quiescent. This action improves theresulting weld bead and the efficiency of the welding operation. Tocontrol the weld puddle, adjacent waveforms generated by the wave shaperhave different shapes to control the length of time during which a givenpolarity relationship exist between the adjacent electrodes. In otherwords, the time that the waveforms of adjacent electrodes have likepolarity or opposite polarity is limited by using different shapes anddifferent relationships between the two adjacent AC waveforms generatedby the waveform technology using a wave shaper or waveform generator.

As so far described, the technology used in practicing the presentinvention is explained in detail. The technology in FIGS. 1–16 isemployed in the preferred embodiment of the present invention. Theinvention involves an electric arc welder schematically illustrated inFIGS. 17 and 18 and involves tandem electric arc welding wherein firstelectrode El and second electrode E2 are connected in modified series.The subsequent electrodes, one of which is illustrated as electrode E3,are driven in unison with electrodes E1 and E2 and perform a tandemwelding process. Of course, several trailing electrodes E3 are normallyused. Only one trailing electrode E3 is illustrated and the samedisclosure relates to the other anticipated trailing electrodes. Thetechnology described in FIGS. 1–16 is applicable to electric arc welder700 used to deposit metal in groove 702 of workpiece W. In theillustrated embodiment, the workpiece W is spaced plates 710, 712 with asmall gap b where edges 714, 716 define trough 704 in plate B having anangle 718, best shown in FIG. 18. Electrodes E1, E2 are arranged, asshown in FIG. 17, and are directed toward a point in groove 704, bestshown in FIG. 18. This point is below the electrical contact 750 anddefines a stickout h. Referring now more specifically to FIG. 17,mechanism 720 drives lead electrodes E1, E2 along groove 702 andincludes a main power source 722, with output terminals 724, 726 todirect AC current by way of leads 730, 732 to the respective electrodesE1, E2. The electrodes are supplied from spool 740, 742, respectively,and are driven through contacts 750, 752 by standard wire feeders 760,762, respectively. Wire feeder 760 includes drive rolls 760 a, 760 brotated by a motor 760 c. In a like manner, wire feeder 762 includesdrive rolls 762 a, 762 b rotated by motor 762 c. Leads 760 d and 762 dare both powered by a control signal in line 764 from main power source722. The power source is a Power Wave unit sold by The Lincoln ElectricCompany of Cleveland, Ohio and is generally disclosed in BlankenshipU.S. Pat. No. 5,278,390. Power source 722 is used to control both wirefeeders 760, 762. This results in a limitation, since a single signal isavailable from the power source to drive the wire feeder. When thisoccurs, the signal on line 764 must be a compromise signal between thedesired wire feed speed of electrodes E1, E2. In practice, the singlesignal on line 764 drives both wire feeders. Of course, software couldbe developed for providing separate controls for the individual wirefeeders at a substantial cost. Separate signals for the wire feeder arecreated when using two power sources, as shown in FIGS. 20 and 21. Lead732 is connected to contact 752 by line 734 and to workpiece W by line736. Thus, current flow between electrode E1 and power source 722 isthrough a low resistance line 734 and a higher resistance line 736. Theresistance of these return paths divides the current flow to adjust theheat in the arc and penetration by the arc force in the welding process.By using the mechanism 720, high deposition by using two serieselectrodes is accomplished at low heat. A limited amount of currentflows from electrode E1 into the workpiece during the welding operation.This welding process is controllable in accordance with the presentinvention, by the circuit schematically illustrated in FIG. 19.

In accordance with the preferred embodiment of the invention, electrodesE1, E2 are trailed by at least one electrode E3, shown in FIG. 17. Thistrailing electrode is driven by mechanism 770 in unison with electrodesE1, E2 even though they may be moved by different mechanisms. In thepreferred embodiment, the same moving device is used for mechanisms 720,770. The trailing electrode mechanism includes auxiliary power source772 which is also a Power Wave unit manufactured by The Lincoln ElectricCompany of Cleveland, Ohio. This power source has output terminals 774,776 for directing an AC current waveform by way of lines 780, 782 to useelectrode E3 in a welding process. Electrode E3 is supplied by spool 784and is driven through contact 786 by wire feeder 790, similar to wirefeeders 760, 762. Wire feeder 790 has spaced drive rolls 790 a, 790 brotated by a motor 790. A control signal from power source 772 in line792 drives motor 790 c to feed electrode E3 toward workpiece W at aspeed determined by the signal in line 792.

In operation of the preferred embodiment illustrated in FIGS. 17 and 18,electrodes E1, E2 and trailing electrode E3 create a weld puddle 800 ingroove 702. Electrodes E1, E2 create a first root pass 802, which beadjoins or tacks edges 714, 716 together by melting the inwardlyprojecting portion of groove 702. Thereafter, puddle 800 is enlarged byoverlaying bead 804 by trailing electrode E3. In practice, furtherelectrodes are used to fill groove 702 in a tandem welding processdisclosed in FIGS. 1–16. In practice, electrode E3 is used in asubmerged arc welding process utilizing a flux dispenser 810 in front ofelectrode E3 and having a dispensing motor 812 for dispensing flux Ffrom hopper 814 through tube 816 in accordance with standard submergedwelding technology. Of course, electrode E1, E2 also are used in asubmerged arc AC welding process. A similar flux dispenser 810 is thenprovided above groove 702 in front of electrode E1. In practice, ashielding gas has also been employed around electrodes E1, E2. Thepresent invention utilizes a power wave power source for the main powersource 722 and for the auxiliary power source 772. These power sourcesare digitally controlled and utilize a waveform technology pioneered byThe Lincoln Electric Company whereby the power sources create waveformsthat comprise a series of individual current pulses created at a highswitching speed in excess of 18 kHz and preferably substantially greaterthan 20 kHz. In practice, the waveforms are provided by a series ofcurrent pulses created at a rate of over 40 kHz. In this manner, the ACcurrent of mechanism 720 and mechanism 770 are provided with any ACwaveform to optimize the welding process for the lead electrodes as wellas the trailing electrodes. This type of welding process isschematically illustrated in FIG. 19, which represents the power sourceused in practicing the preferred embodiment of the present invention.

System 900 of the present invention is schematically illustrated in FIG.19 wherein a Power Wave power source 910 has a high switching outputstage 912 with an input rectifier 914 for receiving three phase linecurrent L1, L2, and L3, and output terminals 912 a and 912 b. Outputstage 912 creates an AC waveform at output terminals 912 a, 9112 b toperform an AC arc welding process at weld station WP illustrated asincluding electrode 920 and workpiece 922 and having a current shunt 930to output a signal in line 932. This signal represents the current ofthe welding process being performed at weld station WP. Comparator 940receives the signal on line 932 and has an output 940 a with a voltagecontrolling pulse width modulator circuit 942, which can be digital oranalog and has a variety of configurations. The pulse width modulator isdriven at high speed by oscillator 944 which, in practice, operates at afrequency of about 40 kHz. This frequency of the oscillator driving thepulse width modulator and provides a series of current pulses at a highspeed switching rate to create an AC waveform at station WP. Thepolarity of the waveform is controlled by the logic or signal fromnetwork 950 having an input line 952 from waveform generator 960 and anoutput line 954 for controlling the polarity of the waveform outputtedfrom stage 912 of the Power Wave power source unit. The profile of thewaveform comprising a series of rapidly created pulses is controlled anddictated by waveform generator 960 having a select network 962 whichselects the desired waveform to be created at output terminals 912 a,912 b of stage 912. By the selected waveform from network 962, thedesired waveform is created for use by the electric arc weldingmechanisms 720 and 770. In accordance with the invention, the waveformbetween electrodes E1, E2 is adjusted as shown in system 900. Thewaveform of the trailing electrode, illustrated as electrode E3, iscontrolled by the circuits illustrated and discussed with respect toFIGS. 1–16. To control the waveform used for the series connectedelectrodes E1, E2, system 900 includes waveform adjusting circuits972–978, each having adjusting networks 972 a–978 a. Circuit 972 adjuststhe frequency of the waveform. After the waveform is selected by network962, a signal from circuit 972 adjusts the frequency of the AC waveform.In a like manner, the duty cycle of the waveform is controlled bycircuit 974. Duty cycle is the relative time the waveform is in thepositive polarity compared to the time in the negative polarity.Circuits 976 and 978 control the magnitude of the current during thenegative portion of the waveform or the positive portion of thewaveform. Circuit 976 is to adjust the magnitude of the negative portionof the waveform. Circuit 978 adjusts the magnitude of the positiveportion of the waveform. The waveform used for electrodes E1, E2 is anAC wave form. However, a DC waveform could be used for a trailingelectrode E3, although AC current is preferred. Indeed, it is preferredto use an AC waveform for all electrodes of electric arc welder 700.Other circuits have been used to adjust the signal on line 970 tomodulate and change the profile of the wave shape selected by network962 to optimize welding at the intersection of electrodes E1, E2.

To increase the amount of current available for the welder shown in FIG.17 using the system shown in FIG. 19, a modified electric arc welder 980is shown in FIG. 20. Only the leading series connected electrodes E1, E2are illustrated; however, trailing electrodes E3 would be employed inwelder 980. The welder is used to obtain more welding current by formingmain power source 722 into a modified power source 722 a including twoseparate Power Wave units 982, 984. These units are connected inparallel to double the current capacity. Output leads 982 a, 982 b areconnected to terminals 724, 726, respectively. Output leads 984 a, 984 bare also connected to terminals 724, 726, respectively. Thus, welder 980operates as welder 700 shown in FIGS. 17 and 18 by using system 900shown in FIG. 19. By using parallel power sources, the available currentis increased, without increasing the capacity of the individual powersource. Furthermore, modules 982, 984 generate their own wire feedercontrol signals in lines 982 c, 984 c, respectively. Thus, wire feeders760, 762 are controlled by separately adjustable signals available ineach of the two power sources 982 and 984. Thus, the individual wirefeed speed of electrodes E1, E2 are adjusted using welder 980. A similarmodification of the preferred embodiment illustrated in FIGS. 17–19 isschematically illustrated in FIG. 21 which shows tandem electrode welder990 including a main power source 992 and a second power source 994. Themain power source 992 has output terminals 996 a and 996 b. Theseterminals are connected to leads 992 a and 992 b, respectively. Lead 992a connects the one output of power source 992 to contact 750 ofelectrode E1. Line 992 b is connected to line 1000 for current flow in apath to and from contact E2. To connect terminal 996 b in the path ofthe workpiece ground, second power source 994 is connected in seriesbetween terminal 996 b and workpiece W. Power source 994 has terminals998 a, 998 b. In this manner, second power source 994 is in series withthe lead 994 b connected to terminal 998 b. In this architecture,electrode E1 carries full current and the current to and from electrodeE1 is divided between electrode E2 and lead 994 b. This is like thearchitecture of FIG. 16. However, lead 994 a from terminal 998 a isconnected to lead 992 b from power source 992. Consequently, the twopower sources 992 and 994 are connected in series between the ground 994b and lead 992 a. Between the two power sources, lead 1000 is connectedto contact 752 of electrode E2. Consequently, electrodes E1 and E2 arein series with a ground current path through Power Wave power source994. By using this arrangement, the waveforms used for both power source992 and 994 are the same and are each created by a system 900 as shownin FIG. 19. Adjustments are made to the waveform process by power source994 to control the current flowing in the ground path of the weldershown in FIG. 21. Since two separate power sources are employed, wirefeeder 760 is controlled by the signal on line 992 c from power source992. A second wire feeder signal in line 994 c is controlled by powersource 994. As discussed with respect to the welder shown in FIG. 20,welder 990 has the advantage of being able to control wire feeders 760,762 separately without complex software in the power source digitalcontrol section. In essence, FIG. 20 shows a main power source with twoparallel modules. In FIG. 21 series connected modules are used; however,the second module is connected in series with the ground line to bettercontrol the current waveform in the ground return circuit or path.

The various technology concepts in FIGS. 1–16 can be applied to thewelder shown in FIGS. 16–21 and the various concepts in these lattermentioned welders can be incorporated into each other to accomplish theobjective of a tandem arc welder wherein the front two electrodes areconnected in series and having a current return path through theworkpiece.

1. An electric arc welder for depositing weld metal along a groovebetween two edges of a metal workpiece, said welder comprising a firstelectrode driven by a first wire feeder toward a point in said groove, asecond electrode driven by a second wire feeder toward said point and amain power source with a first output terminal connected to said firstelectrode and a second output terminal connected both to said secondelectrode and directly or indirectly to said metal workpiece to create asecond electrode path and a workpiece path, said power source includinga high speed switching output stage for creating current with a selectedAC waveform between said first and second output terminals, saidwaveform of said main power source having an independently adjustablefrequency unrelated to a line frequency of line voltage provided to themain power source and said waveform being generated by a waveformgenerator controlling a pulse width modulator circuit to determine thecurrent operation of said output stage and a device for moving saidelectrodes in unison along said groove in a given direction.
 2. Anelectric arc welder, as defined in claim 1, including a third electrodebehind said first and second electrodes and generally movable with saidfirst and second electrodes, said third electrode powered by anauxiliary power source separate from said main power source with a firstoutput terminal connected to said third electrode and a second outputterminal connected to said workpiece.
 3. An electric arc welder asdefined in claim 2 wherein said auxiliary power source includes a highspeed switching output stage for creating a selected trailing waveformbetween said first and second output terminals of said auxiliary powersource, said trailing waveform of said auxiliary power source generatedby a waveform generator controlling a pulse width modulator circuit todetermine the current operation of said output stage of said auxiliarypower source.
 4. An electric arc welder, as defined in claim 3, whereinsaid trailing waveform is an AC waveform.
 5. An electric arc welder asdefined in claim 4 wherein said main power source includes a first andsecond module power source connected in parallel with said outputterminals of said main power source.
 6. An electric arc welder asdefined in claim 4 including a second power source in series betweensaid second electrode and said metal workpiece to create said workpiecepath for said second output terminal of the main power source.
 7. Anelectric arc welder as defined in claim 6 wherein said second powersource has a current output with said selected AC waveform.
 8. Anelectric welder, as defined in claim 3 wherein said trailing waveform isa DC waveform.
 9. An electric arc welder as defined in claim 8 whereinsaid main power source includes a first and second module power sourceconnected in parallel with said output terminals of said main powersource.
 10. An electric arc welder as defined in claim 8 including asecond power source in series between said second electrode and saidmetal workpiece to create said workpiece path for said second outputterminal of the main power source.
 11. An electric arc welder as definedin claim 10 wherein said second power source has a current output withsaid selected AC waveform.
 12. An electric arc welder as defined inclaim 8 including a flux dispenser in front of said third electrode. 13.An electric arc welder as defined in claim 3 wherein said main powersource includes a first and second module power source connected inparallel with said output terminals of said main power source.
 14. Anelectric arc welder as defined in claim 13 including a flux dispenser infront of said third electrode.
 15. An electric arc welder as defined inclaim 13 wherein said waveform generator of said main power sourceincludes a circuit to adjust the frequency of said AC waveform.
 16. Anelectric arc welder as defined in claim 13 wherein said waveformgenerator of said main power source includes a circuit to adjust theduty cycle of said AC waveform.
 17. An electric arc welder as defined inclaim 13 wherein said main power source includes a circuit to adjust thepercentage of the positive portion of said AC waveform compared to saidnegative portion of said AC waveform.
 18. An electric arc welder asdefined in claim 3 including a second power source in series betweensaid second electrode and said metal workpiece to create said workpiecepath for said second output terminal of the main power source.
 19. Anelectric arc welder as defined in claim 18 wherein said second powersource has a current output with said selected AC waveform.
 20. Anelectric arc welder as defined in claim 18 wherein said waveformgenerator of said main power source includes a circuit to adjust thefrequency of said AC waveform.
 21. An electric arc welder as defined inclaim 18 wherein said waveform generator of said main power sourceincludes a circuit to adjust the duty cycle of said AC waveform.
 22. Anelectric arc welder as defined in claim 18 wherein said main powersource includes a circuit to adjust the percentage of the positiveportion of said AC waveform compared to said negative portion of said ACwaveform.
 23. An electric arc welder as defined in claim 3 including aback plate below said groove and under said workpiece.
 24. An electricarc welder as defined in claim 23 wherein said waveform generator ofsaid main power source includes a circuit to adjust the frequency ofsaid AC waveform.
 25. An electric arc welder as defined in claim 23wherein said waveform generator of said main power source includes acircuit to adjust the duty cycle of said AC waveform.
 26. An electricarc welder as defined in claim 23 wherein said main power sourceincludes a circuit to adjust the percentage of the positive portion ofsaid AC waveform compared to said negative portion of said AC waveform.27. An electric arc welder as defined in claim 3 including a fluxdispenser in front of said third electrode.
 28. An electric arc welderas defined in claim 27 wherein said waveform generator of said mainpower source includes a circuit to adjust the frequency of said ACwaveform.
 29. An electric arc welder as defined in claim 27 wherein saidwaveform generator of said main power source includes a circuit toadjust the duty cycle of said AC waveform.
 30. An electric arc welder asdefined in claim 27 wherein said main power source includes a circuit toadjust the percentage of the positive portion of said AC waveformcompared to said negative portion of said AC waveform.
 31. An electricarc welder as defined in claim 3 wherein said waveform generator of saidmain power source includes a circuit to adjust the frequency of said ACwaveform.
 32. An electric arc welder as defined in claim 3 wherein saidwaveform generator of said main power source includes a circuit toadjust the duty cycle of said AC waveform.
 33. An electric arc welder asdefined in claim 3 wherein said main power source includes a circuit toadjust the percentage of the positive portion of said AC waveformcompared to said negative portion of said AC waveform.
 34. An electricarc welder as defined in claim 2 wherein said main power source includesa first and second module power source connected in parallel with saidoutput terminals of said main power source.
 35. An electric arc welderas defined in claim 34 wherein said first wire feeder is driven by saidfirst module power source and said second wire feeder is driven by saidsecond module power source.
 36. An electric arc welder as defined inclaim 34 including a back plate below said groove and under saidworkpiece.
 37. An electric arc welder as defined in claim 34 including aflux dispenser in front of said third electrode.
 38. An electric arcwelder as defined in claim 34 wherein said waveform generator of saidmain power source includes a circuit to adjust the frequency of said ACwaveform.
 39. An electric arc welder as defined in claim 34 wherein saidwaveform generator of said main power source includes a circuit toadjust the duty cycle of said AC waveform.
 40. An electric arc welder asdefined in claim 34 wherein said main power source includes a circuit toadjust the percentage of the positive portion of said AC waveformcompared to said negative portion of said AC waveform.
 41. An electricarc welder as defined in claim 2 including a second power source inseries between said second electrode and said metal workpiece to createsaid workpiece path for said second output terminal of the main powersource.
 42. An electric arc welder as defined in claim 41 wherein saidfirst wire feeder is driven by said main power source and said secondwire feeder is driven by said second power source.
 43. An electric arcwelder as defined in claim 42 wherein said second power source has acurrent output with said selected AC waveform.
 44. An electric arcwelder as defined in claim 41 wherein said second power source has acurrent output with said selected AC waveform.
 45. An electric arcwelder as defined in claim 41 including a back plate below said grooveand under said workpiece.
 46. An electric arc welder as defined in claim41 including a flux dispenser in front of said third electrode.
 47. Anelectric arc welder as defined in claim 41 wherein said waveformgenerator of said main power source includes a circuit to adjust thefrequency of said AC waveform.
 48. An electric arc welder as defined inclaim 41 wherein said waveform generator of said main power sourceincludes a circuit to adjust the duty cycle of said AC waveform.
 49. Anelectric arc welder as defined in claim 41 wherein said main powersource includes a circuit to adjust the percentage of the positiveportion of said AC waveform compared to said negative portion of said ACwaveform.
 50. An electric arc welder as defined in claim 2 including aback plate below said groove and under said workpiece.
 51. An electricarc welder as defined in claim 50 including a flux dispenser in front ofsaid third electrode.
 52. An electric arc welder as defined in claim 50wherein said waveform generator of said main power source includes acircuit to adjust the frequency of said AC waveform.
 53. An electric arcwelder as defined in claim 50 wherein said waveform generator of saidmain power source includes a circuit to adjust the duty cycle of said ACwaveform.
 54. An electric arc welder as defined in claim 50 wherein saidmain power source includes a circuit to adjust the percentage of thepositive portion of said AC waveform compared to said negative portionof said AC waveform.
 55. An electric arc welder as defined in claim 2including a flux dispenser in front of said third electrode.
 56. Anelectric arc welder as defined in claim 55 wherein said waveformgenerator of said main power source includes a circuit to adjust thefrequency of said AC waveform.
 57. An electric arc welder as defined inclaim 55 wherein said waveform generator of said main power sourceincludes a circuit to adjust the duty cycle of said AC waveform.
 58. Anelectric arc welder as defined in claim 55 wherein said main powersource includes a circuit to adjust the percentage of the positiveportion of said AC waveform compared to said negative portion of said ACwaveform.
 59. An electric arc welder as defined in claim 2 wherein saidwaveform generator of said main power source includes a circuit toadjust the frequency of said AC waveform.
 60. An electric arc welder asdefined in claim 2 wherein said waveform generator of said main powersource includes a circuit to adjust the duty cycle of said AC waveform.61. An electric arc welder as defined in claim 2 wherein said main powersource includes a circuit to adjust the percentage of the positiveportion of said AC waveform compared to said negative portion of said ACwaveform.
 62. An electric arc welder as defined in claim 1 wherein saidauxiliary power source includes a high speed switching output stage forcreating a selected trailing waveform between said first and secondoutput terminals of said auxiliary power source, said trailing waveformof said auxiliary power source generated by a waveform generatorcontrolling a pulse width modulator circuit to determine the currentoperation of said output stage of said auxiliary power source.
 63. Anelectric arc welder, as defined in claim 62, wherein said trailingwaveform is an AC waveform.
 64. An electric arc welder as defined inclaim 63 wherein said main power source includes a first and secondmodule power source connected in parallel with said output terminals ofsaid main power source.
 65. An electric arc welder as defined in claim63 including a second power source in series between said secondelectrode and said metal workpiece to create said workpiece path forsaid second output terminal of the main power source.
 66. An electricarc welder as defined in claim 65 wherein said second power source has acurrent output with said selected AC waveform.
 67. An electric arcwelder as defined in claim 63 wherein said waveform generator of saidmain power source includes a circuit to adjust the frequency of said ACwaveform.
 68. An electric arc welder as defined in claim 63 wherein saidwaveform generator of said main power source includes a circuit toadjust the duty cycle of said AC waveform.
 69. An electric arc welder asdefined in claim 63 wherein said main power source includes a circuit toadjust the percentage of the positive portion of said AC waveformcompared to said negative portion of said AC waveform.
 70. An electricwelder, as defined in claim 62 wherein said trailing waveform is a DCwaveform.
 71. An electric arc welder as defined in claim 70 wherein saidmain power source includes a first and second module power sourceconnected in parallel with said output terminals of said main powersource.
 72. An electric arc welder as defined in claim 70 including asecond power source in series between said second electrode and saidmetal workpiece to create said workpiece path for said second outputterminal of the main power source.
 73. An electric arc welder as definedin claim 72 wherein said second power source has a current output withsaid selected AC waveform.
 74. An electric arc welder as defined inclaim 62 wherein said main power source includes a first and secondmodule power source connected in parallel with said output terminals ofsaid main power source.
 75. An electric arc welder as defined in claim62 including a second power source in series between said secondelectrode and said metal workpiece to create said workpiece path forsaid second output terminal of the main power source.
 76. An electricarc welder as defined in claim 75 wherein said second power source has acurrent output with said selected AC waveform.
 77. An electric arcwelder as defined in claim 62 wherein said waveform generator of saidmain power source includes a circuit to adjust the frequency of said ACwaveform.
 78. An electric arc welder as defined in claim 62 wherein saidwaveform generator of said main power source includes a circuit toadjust the duty cycle of said AC waveform.
 79. An electric arc welder asdefined in claim 62 wherein said main power source includes a circuit toadjust the percentage of the positive portion of said AC waveformcompared to said negative portion of said AC waveform.
 80. An electricarc welder as defined in claim 1 wherein said main power source includesa first and second module power source connected in parallel with saidoutput terminals of said main power source.
 81. An electric arc welderas defined in claim 80 wherein said first wire feeder is driven by saidfirst module power source and said second wire feeder is driven by saidsecond module power source.
 82. An electric arc welder as defined inclaim 80 including a back plate below said groove and under saidworkpiece.
 83. An electric arc welder as defined in claim 80 whereinsaid waveform generator of said main power source includes a circuit toadjust the frequency of said AC waveform.
 84. An electric arc welder asdefined in claim 80 wherein said waveform generator of said main powersource includes a circuit to adjust the duty cycle of said AC waveform.85. An electric arc welder as defined in claim 80 wherein said mainpower source includes a circuit to adjust the percentage of the positiveportion of said AC waveform compared to said negative portion of said ACwaveform.
 86. An electric arc welder as defined in claim 1 including asecond power source in series between said second electrode and saidmetal workpiece to create said workpiece path for said second outputterminal of the main power source.
 87. An electric arc welder as definedin claim 86 wherein said first wire feeder is driven by said main powersource and said second wire feeder is driven by said second powersource.
 88. An electric arc welder as defined in claim 87 wherein saidsecond power source has a current output with said selected AC waveform.89. An electric arc welder as defined in claim 86 wherein said secondpower source has a current output with said selected AC waveform.
 90. Anelectric arc welder as defined in claim 86 including a back plate belowsaid groove and under said workpiece.
 91. An electric arc welder asdefined in claim 86 wherein said waveform generator of said main powersource includes a circuit to adjust the frequency of said AC waveform.92. An electric arc welder as defined in claim 86 wherein said waveformgenerator of said main power source includes a circuit to adjust theduty cycle of said AC waveform.
 93. An electric arc welder as defined inclaim 86 wherein said main power source includes a circuit to adjust thepercentage of the positive portion of said AC waveform compared to saidnegative portion of said AC waveform.
 94. An electric arc welder asdefined in claim 1 including a back plate below said groove and undersaid workpiece.
 95. An electric arc welder as defined in claim 94wherein said waveform generator of said main power source includes acircuit to adjust the frequency of said AC waveform.
 96. An electric arcwelder as defined in claim 94 wherein said waveform generator of saidmain power source includes a circuit to adjust the duty cycle of said ACwaveform.
 97. An electric arc welder as defined in claim 94 wherein saidmain power source includes a circuit to adjust the percentage of thepositive portion of said AC waveform compared to said negative portionof said AC waveform.
 98. An electric arc welder as defined in claim 1wherein said waveform generator of said main power source includes acircuit to adjust the frequency of said AC waveform.
 99. An electric arcwelder as defined in claim 1 wherein said waveform generator of saidmain power source includes a circuit to adjust the duty cycle of said ACwaveform.
 100. An electric arc welder as defined in claim 1 wherein saidmain power source includes a circuit to adjust the percentage of thepositive portion of said AC waveform compared to said negative portionof said AC waveform.
 101. An electric arc welder for depositing weldmetal along a groove between two edges of a metal workpiece, said weldercomprising: a first electrode driven by a first wire feeder at a firstwire feed speed toward a point in said groove; a second electrode drivenby a second wire feeder at a second wire feed speed toward said point,said first and second wire feed speeds being separately controlled; amain power source with a first output terminal connected to said firstelectrode and a second output terminal connected to said secondelectrode to create a series electrode path, said power source includinga high speed switching output stage for creating current with a selectedwaveform between said first and second output terminals, said waveformof said main power source having an independently adjustable frequencyunrelated to a line frequency of line voltage provided to the main powersource and said waveform being generated by a waveform generatorcontrolling a pulse width modulator circuit to determine the currentoperation of said main power source; and a device for moving saidelectrodes in unison along said groove in a given direction.
 102. Anelectric arc welder as defined in claim 101, wherein said second outputterminal is further connected directly or indirectly to said metalworkpiece to create a workpiece path.
 103. An electric arc welder asdefined in claim 102, wherein said selected waveform is an AC waveform.104. An electric arc welder as defined in claim 103 including a secondpower source in series between said second electrode and said metalworkpiece to create said workpiece path for said second output terminalof the main power source.
 105. An electric arc welder as defined inclaim 104 wherein said first wire feeder has a speed control signalcreated by said main power source and said second wire feeder has aspeed control signal created by said second power source.
 106. Anelectric arc welder as defined in claim 102 including a second powersource in series between said second electrode and said metal workpieceto create said workpiece path for said second output terminal of themain power source.
 107. An electric arc welder as defined in claim 106wherein said first wire feeder has a speed control signal created bysaid main power source and said second wire feeder has a speed controlsignal created by said second power source.
 108. An electric arc welderas defined in claim 101, wherein said selected waveform is an ACwaveform.
 109. An electric arc welder as defined in claim 108 includinga second power source in series between said second electrode and saidmetal workpiece to create a workpiece path for said second outputterminal of the main power source.
 110. An electric arc welder asdefined in claim 109 wherein said first wire feeder has a speed controlsignal created by said main power source and said second wire feeder hasa speed control signal created by said second power source.
 111. Anelectric arc welder as defined in claim 101 including a second powersource in series between said second electrode and said metal workpieceto create a workpiece path for said second output terminal of said mainpower source.
 112. An electric arc welder as defined in claim 111wherein said first wire feeder has a speed control signal created bysaid main power source and said second wire feeder has a speed controlsignal created by said second power source.
 113. An electric arc welderas defined in claim 101, wherein the first and second wire feed speedsare different.
 114. An electric arc welder for depositing weld metalalong a groove between two edges of a metal workpiece, said weldercomprising: a first electrode driven at a first wire feed speed by afirst wire feeder toward a point in said groove; a second electrodedriven at a second wire feed speed by a second wire feeder toward saidpoint; a first power source with an output terminal connected to saidfirst electrode; and a second power source with an output terminalconnected to said second electrode, said electrodes and power sourcesbeing connected to form a series circuit path with said power sourcesproviding current in said series circuit path for depositing weld metalalong said workpiece groove, said first wire feeder being driven by oneof said power sources to control said first wire feed speed, and saidsecond wire feeder being driven by the other of said power sources tocontrol said second wire feed speed.
 115. An electric arc welder asdefined in claim 114, wherein said first wire feeder is driven by one ofsaid power sources to control said first wire feed speed, and saidsecond wire feeder is driven by the other of said power sources tocontrol said second wire feed speed.
 116. An electric arc welder asdefined in claim 115, wherein said first power source drives said secondwire feeder to control said second wire feed speed and said second powersource drives said first wire feeder to control said first wire feedspeed.
 117. An electric arc welder as defined in claim 116, wherein saidfirst and second wire feed speeds are different.
 118. An electric arcwelder as defined in claim 116, wherein one of said power sourcesincludes another terminal connected to said workpiece.
 119. An electricarc welder as defined in claim 115, wherein said first power sourcedrives said first wire feeder to control said first wire feed speed andsaid second power source drives said second wire feeder to control saidsecond wire feed speed.
 120. An electric arc welder as defined in claim119, wherein said first and second wire feed speeds are different. 121.An electric arc welder as defined in claim 119, wherein one of saidpower sources includes another terminal connected to said workpiece.122. An electric arc welder as defined in claim 115, wherein said firstand second wire feed speeds are different.
 123. An electric arc welderas defined in claim 122, wherein one of said power sources includesanother terminal connected to said workpiece.
 124. An electric arcwelder as defined in claim 115, wherein one of said power sourcesincludes another terminal connected to said workpiece.
 125. An electricarc welder as defined in claim 115, wherein at least one of said powersources includes a high speed switching output stage for creatingcurrent with a selected waveform in said series circuit path, saidwaveform having an independently adjustable frequency unrelated to aline frequency of line voltage provided to the main power source andsaid waveform being generated by a waveform generator controlling apulse width modulator circuit to determine the current operation of saidat least one of said power sources.